Propeller driven fixed wing aircraft typically have an optimal level flight cruising speed at which the airplane's air speed and the airplane's rate of fuel consumption are deemed to be acceptable in relation to each other. At speeds above an aircraft's optimal cruising speed, the benefits of reduced transit time are viewed as being negatively “outweighed” by the corresponding reduction in fuel economy. Conversely, at air speeds below the aircraft's optimal cruising speed, the resultant benefit of increased fuel economy is viewed as being negatively “outweighed” by the corresponding increase in transit time. Accordingly, an airplane's optimal cruising speed may vary from time to time as the result of changing demands of passengers on transit time and the price of aircraft fuel.
For small aircraft (Such as, for example, a fixed wing turbo-prop aircraft, capable of carrying up to nine passengers, and approved for operation by a single pilot) a single turbo-prop engine is typically capable of maintaining the aircraft in level flight at such an optimal cruising speed which balances fuel costs and time costs. For such an aircraft, optimal cruising speeds are typically sub-sonic speeds ranging between 200 and 400 mph. Omitting safety considerations, for the sake of enhanced fuel economy it is often desirable that an aircraft's optimal cruising speed be maintained by a minimum number of engines. For small aircraft, such minimum number typically is one.
However, a problem or deficiency associated with providing such small exemplary aircraft with a non-redundant or single turbo-prop engine is recognized in situations where flying conditions create a need for forward thrust over and above that which is normally needed for maintaining the optimal cruising speed. Examples of such flying conditions include the increased power demands of aircraft icing, and climbing in altitude to clear terrain obstructions or adverse weather conditions. In such circumstances, a single turbo-prop engine may have insufficient reserve power over its normal optimal cruising speed power to maintain flight. A further drawback or deficiency related to such provision of a single turbo-prop engine may be catastrophically recognized upon an engine failure which requires an unpowered glide to landing in order to avoid a crash.
In the design of small aircraft, the above described drawbacks and deficiencies associated with non-redundant provisions of a single turbo-prop engine are typically recognized as grossly overriding the fuel efficiency benefits of such single engines. Accordingly, such small aircraft are often negatively affected by design compromises wherein left and right wing mounted “tractor” turbo-prop engines are provided, or wherein left and right wing mounted “pusher” configured turbo-prop engines are provided. In order for such dual or left and right turbo-prop engines to provide adequate power supply redundancy in the case of an engine failure, each of such engines is typically sized sufficiently large to independently maintain the aircraft in level flight and to further compensate for impaired aerodynamics (e.g., from hard left or right rudder) which typically results from a lateral thrust imbalance.
Provision of such dual turbo-prop engines markedly reduces the airplane's fuel economy below that which is achievable by the exemplary single turbo-prop aircraft described above. While such twin turbo-prop aircraft typically have a higher normal cruising speed than single turbo-prop aircraft, such additional speed is attained at a cost of reduced fuel efficiency. Accordingly, such typical provision of redundant turbo-prop engines in a small fixed wing aircraft often constitutes a less than desirable safety/fuel efficiency design compromise.
The instant inventive fixed wing aircraft solves or ameliorates the above discussed problems and deficiencies of both single engine turbo-prop aircraft and turbo-prop aircraft having engine redundancy, while preserving the benefits of both. Such benefits are attained by configuring the inventive aircraft to include a preferably rearwardly mounting “pusher” turbo-prop engine, such engine being redundantly backed up and/or assisted by a nose mounted, and preferably alternately extendable and retractable, auxiliary jet engine.